1. Field of the Invention
This invention relates generally to a system, method and apparatus for providing an ophthalmic lens, and more particularly, to a lens, system and method having at least one rotationally asymmetric diffractive structure.
2. Description of the Related Art
Surgery on the human eye has become commonplace in recent years. Many patients pursue eye surgery as an elective procedure, such as to avoid the use of contacts or glasses. Other patients pursue surgery to correct an adverse condition in the eye. Such adverse conditions may include, for example, cataracts or presbyopia, as well as other conditions known to those skilled in the art that may adversely affect elements of the eye.
The anatomy and physiology of the human eye is well understood. Generally speaking, the structure of the human eye includes an outer layer formed of two parts, namely the cornea and the sclera. The middle layer of the eye includes the iris, the choroid, and the ciliary body. The inner layer of the eye includes the retina. The eye also includes, physically associated with the middle layer, a crystalline lens that is contained within an elastic capsule, also referred to as the lens capsule, or capsular bag. Image formation in the eye occurs by entry of image-forming light to the eye through the cornea, and refraction by the cornea and the crystalline lens to focus the image-forming light on the retina. The retina provides the light sensitive tissue of the eye.
Ophthalmic lenses, such as intraocular lenses (IOLs), phakic IOLs and corneal implants may be used to enhance or correct vision, such as to correct for the aforementioned adverse conditions, including aberrations or inadequacies that adversely affect the performance of the referenced structures of the eye. For example, IOLs are routinely used to replace the crystalline lens of an eye that is removed during cataract surgery.
By way of example, an ophthalmic lens in the form of an IOL may be spheric/aspheric or toric. Spheric/aspheric IOLs may be used for correction of a myriad of vision problems, while toric IOLs are typically used specifically for astigmatic eye correction. Generally, astigmatism is an optical defect in which vision is blurred due to the ocular inability to focus a point object into a sharply focused image on the retina. This may be due to an irregular, or toric, curvature of the cornea and/or eye lens. When using an IOL, the angular orientation of the IOL in the eye is of particular importance since a toric IOL is intended to be inserted at a specific angle. If the insertion angle is not correct and/or maintained, any preoperative astigmatism will not be fully corrected, and in fact the astigmatic condition may worsen. The condition caused by this misalignment of the IOL is often referred to as residual cylinder, or remaining astigmatism.
More particularly, toric IOLs are generally to be positioned in the eye such that the cylinder axis of the IOL is properly aligned with the cylinder axis of the patient's cornea. Thus, ophthalmic lenses, such as IOLs, are typically sensitive to cylinder orientation misalignment relative to that to be corrected, such as wherein the axis of the toric lens in the eye and the lens for correction are not accurately aligned. Further, typical toric lenses are highly sensitive to a mismatch between the intended postoperative refraction and the power of the selected lens. Suboptimal lens designs may arise due to these sensitivities based on measurement errors, unintended changes of cylinder power and/or axis during or after surgery, or because lenses are offered only in a number of discrete cylinder increments and/or powers.
Thus, a need exists for a lens apparatus, system and method that improve the performance of toric ophthalmic lenses.